Gallium Phosphide based Tunable Wideband Photodetector with High Responsivity in Vis-NIR

Photodetectors (PDs) are integral components in the realms of optical communication, imaging, and sensing technologies. This research reports on the simulation and analysis of a tunable multi-spectrum photodetector predicated on a gallium phosphide (GaP) substrate, which is augmented with thin metallic films of aluminum (Al) and silver (Ag). The work examines the influence of these metallic layers on the optical characteristics of PDs, specifically regarding parameters such as light absorption, reflection, quantum efficiency ($\eta$), and responsivity ($\rho$). Finite-difference time-domain (FDTD) simulations were employed to study the optical interactions occurring within the PD design. The outcomes reveal that the GaP-AI PD exhibits significantly high absorption in the visible spectrum, notably at 457.18 nm (blue), with an absorption coefficient of 0.4129 a.u. and $\eta$ of $27.71 \%$. Further, its absorption diminishes within the near-infrared (NIR) domain. Moreover, the GaP-Ag PD demonstrates enhanced absorption across a range of wavelength bands, attaining peak absorption at 688.94 nm (red) with a value of 0.91086 a.u. and $\eta$ of $55.36 \%$. The value of $\rho$ for the GaP-Ag PD is $0.3076 \text{A} / \text{W}$ in the red spectrum, in contrast to $0.1157 \text{A} / \text{W}$ observed for the GaP-Al variant. These findings imply that GaP-Al PDs are optimally aligned for visible-light applications, including high-resolution imaging and optical sensing, whereas GaP-Ag PDs prove more effective for red and NIR applications, ranging from biomedical imaging and nocturnal vision. The research offers valuable insights into the optimization of PD designs for targeted applications in future optoelectronic devices.